Membrane fatty acid composition and fluidity are involved in the resistance to freezing of Lactobacillus buchneri R1102 and Bifidobacterium longum R0175.

Séverine Louesdon,Marielle Bouix,Catherine Béal,Raphaëlle Tourdot‐Maréchal,Séverine Charlot‐Rougé

doi:10.1111/1751-7915.12132

Abstract

Determinations of membrane fatty acid composition and fluidity were used together with acidification activity and viability measurements to characterize the physiological state after freezing of Lactobacillus buchneri R1102 and Bifidobacterium longum R0175 cells harvested in the exponential and stationary growth phases. For both strains, lower membrane fluidity was achieved in cells harvested in the stationary growth phase. This change was linked to a lower unsaturated-to-saturated fatty acid ratio for both strains and a higher cyclic-to-saturated fatty acid ratio for L. buchneri R1102 alone. These membrane properties were linked to survival and to maintenance of acidification activity of the cells after freezing, which differed according to the strain and the growth phase. Survival of B. longum R0175 was increased by 10% in cells with low membrane fluidity and high relative saturated fatty acid contents, without any change in acidification activity. Acidification activity was more degraded (70 min) in L. buchneri R1102 cells displaying low membrane fluidity and high saturated and cyclic fatty acid levels. Finally, this study showed that membrane modifications induced by the growth phase differed among bacterial strains in terms of composition. By lowering membrane fluidity, these modifications could be beneficial for survival of B. longum R0175 during the freezing process but detrimental for maintenance of acidification activity of L. buchneri R1102.

Highlights

Lactic acid bacteria and bifidobacteria are involved in a number of industrial applications as a result of their metabolic properties and probiotic functionalities (Roy, 2005; Giraffa et al, 2010)
This study aims at better understanding some of the mechanisms that govern the cryotolerance of two strains, L. buchneri R1102 and B. longum R1075 by linking their viability and acidification activity to their membrane characteristics, after harvesting cells in the exponential and stationary phases
Effect of harvesting time on membrane fatty acid composition and fluidity The relative percentages of the membrane fatty acids of L. buchneri R1102 and B. longum R0175 were determined by considering cells recovered in exponential and stationary phases (Table 1)

Summary

Introduction

Lactic acid bacteria and bifidobacteria are involved in a number of industrial applications as a result of their metabolic properties and probiotic functionalities (Roy, 2005; Giraffa et al, 2010). Bifidobacterium longum displays many probiotic benefits such as a reduction of lactose malabsorption, prevention of gastrointestinal and respiratory infections, and modulation of immune response (Aureli et al, 2011; Shiby and Mishra, 2013) Industrial starters of these bacteria are produced by fermentation and stabilized by freezing, freeze-drying or spray-drying under optimal conditions in order to achieve high concentrations of viable and active cells at the end of production and during the storage of the starters (Carvalho et al, 2004; Béal et al, 2008). Since bifidobacteria grow in anaerobic environments and ferment glucose through the bifid shunt, instead of the glycolytic pathway used by lactic acid bacteria, due to of differences in their metabolism, their production conditions are not the same In both cases, exposure to freezing or freeze-drying affects their viability and their metabolic activity as a result of stressful conditions (Fonseca et al, 2001; Jayamanne and Adams, 2006). This study aims at better understanding some of the mechanisms that govern the cryotolerance of two strains, L. buchneri R1102 and B. longum R1075 by linking their viability and acidification activity to their membrane characteristics, after harvesting cells in the exponential and stationary phases

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Conclusion